Among the problems confronting modern industry is the disposition of the large amounts of polymeric scrap materials generated, the major portion of which is not biodegradable nor easily separable into useful components. This is particularly true in the rubber tire industry, where despite the tremendously increasing piles of discarded tires year by year, no effective means have been designed to usefully recycle this material. The present invention, as hereinafter described, provides a practical and profitable outlet for the disposition of elastomer and other scrap from discarded polymeric materials as well as from trimmings and rejects of fabricating plants.
In addition to the foregoing problem for which the present invention offers a solution, it further extends the available processes for the production of composite plastics having unique combinations of physical properties. In the past such composites have been produced by mechanically blending or chemically bonding two or more polymers. For example, acrylonitrile-butadiene-styrene terpolymer (ABS) is produced by grafting polyacrylonitrile (a rigid polymer) onto polystyrene-butadiene (an elastic polymer). A common method for physically combining two materials into a composite is by blending. In this manner, for example, there is produced a blended composite of polybutylene terephthalate with polycarbonate (a very rigid material). However, the known chemical methods of making composite polymers require very precise control of processing conditions in order to produce products of desired uniform characteristics. The available physical alternatives, on the other hand, require good compatibility among the constituent materials to avoid phase separation, which limits the choice of polymers which can be thus combined with one another. It also virtually rules out the blends of highly elastomeric materials with rigid plastics because, most often, these are incompatible. Accordingly, industry is limited in the chemical and physical mixing of polymers to a relatively small number of these substances.
Yet another problem addressed by this invention is to convert a variety of polymeric scrap materials, such as used tires or polyester soda bottles, into useful materials. For want of better means for the disposition, industry has resorted to burning of scrap, which presents tremendous pollution problems, and even use of scrap in landfill is becoming more and more unacceptable.
In accordance with one aspect of the present invention, polymeric scrap materials and other polymers in a finely divided state are chemically modified at their surfaces to provide particles which can be incorporated and combined into a polymeric matrix to provide novel polymeric products of desirable controlled properties. Such chemical modification is effected by treatment of these particles under controlled conditions with fluorine in the presence of another reactive gas, as will hereinafter appear.